Sterile insect technique field trials to eliminate malaria under way

The first South African research trial for the biological control of mosquitoes using the sterile insect technique started in Jozini in KwaZulu-Natal earlier this month, with funding from the Department of Science and Technology.

South Africa is making significant progress in reducing the incidence of malaria, and is now at a level where the country in a prime position to begin with complementary vector control strategies that address the problem of insecticide resistance.

However, indoor residual spraying (IRS) using DDT and pyrethroid insecticides, while effective in controlling the disease, is unlikely to eliminate malaria on its own. IRS targets mainly indoor feeding and resting mosquitoes, and is not effective against vectors that feed and rest outdoors such as Anopheles arabiensis, which is a major contributor to outdoor transmission in South Africa's malaria-affected provinces.

One of the supplementary methods being explored is the use of the sterile insect technique (SIT).This works like birth control to suppress mosquito populations and reduce the spread of malaria. The technique involves the mass-rearing and sterilisation of male mosquitoes before they are released in the wild.

In this instance, mosquitoes are sterilised at the National Institute of Communicable Diseases (NICD), a national public health institute that, among other things, collects, analyses and interprets communicable disease data on an ongoing and systematic basis.

The sterile mosquitoes are then released in infested areas where they mate with females but do not produce offspring. As a result, the technique suppresses and eventually eliminates mosquito populations. As only female mosquitoes "bite", the release of males has no negative effects on the people in the area.

Dr Givemore Munhenga, Senior Medical Scientist at the NICD, says the project has been successfully tested in laboratories and it is the first time in South Africa that these mosquitoes have been released systematically in a wide area.

"We chose Mamfene in Jozini because their control programme is going very well and they have managed to reduce malaria transmission to a level where we can start thinking about a level where malaria is eliminated," he said.

Munhenga points out that community backing is necessary if any public heath intervention is to succeed.The communities are engaged to find out what the people involved know and feel about malaria.If gaps are identified, these are given attention to ensure that execution is smooth.

Ms Nondumiso Mabaso, the Community Engagement Officer at Mamfene, agrees that human behaviour is an important element in malaria control.

"Since I started in 2015," says Mabaso, "the level of understanding of what the community perceives as the cause of malaria, and the extent to which they believe they can prevent and treat malaria, shows the impact of malaria education, and the acceptance and usage of malaria control interventions."

Known as the Sterile Insect Technique for Malaria Mosquitoes in a South African Setting, the initiative is currently coordinated and operated under the auspices of the Nuclear Technologies in Medicine and the Biosciences Initiative (NTeMBI), a platform of the Department of Science and Technology.This is because the mosquitoes are sterilised using irradiation.

The long-term goal of the project is to establish an industrial-scale mass-rearing facility capable of producing sterile male mosquitoes in sufficient numbers to support large-scale, area-wide SIT field programmes in malaria-affected areas in the country and the region.

This is a critical initiative, as it will increase the number of available vector control interventions, while reducing dependency on the use of insecticides, as the country moves towards malaria elimination.

The SIT programme complements related research initiatives in the country, such as the anti-malaria drug discovery programmes of the South African Medical Research Council and the University of Cape Town, among others.

Malaria transmission in South Africa is relatively low, with a case incidence of less than one per 1 000 of the population, and is limited to the low-altitude border regions in Limpopo, Mpumalanga and KwaZulu-Natal. However, despite a concerted effort to eliminate the disease in these provinces, transmission has remained steady over the past decade at approximately 11 000 cases per year. The country is also still prone to epidemics, such as that experienced during the 1999/2000 malaria season, during which approximately 65 000 cases were recorded.